Conductive paste and conductive film musing it, plating method and production method for fine metal component

ABSTRACT

A conductive paste capable of further reducing the electrical resistance of a conductive film or the like, a conductive film having an anisotropic conductivity, a plating method for forming a plated coating having a uniform crystal structure, and a method of producing a fine metal component having good characteristics. A conductive paste is such that metal powder in the form of many fine metal particles being linked in a chain form is blended. A conductive film is such that chain-form metal powder having paramagnetism is oriented in a constant direction by applying a magnetic field to a coating formed by the application of conductive paste. A plating method grows a plated coating by electroplating on a conductive film formed from a conductive paste. A method of producing a fine metal component which selectively grows a plated coating ( 4 ′) on a conductive film ( 1 ) exposed at fine pass-hole pattern portions in a mold ( 3 ) to produce a fine metal component.

TECHNICAL FIELD

[0001] The present invention relates to a new conductive paste, aconductive film formed using the conductive paste, a plating methodusing the conductive paste, and a production method for a fine metalcomponent to which the plating method is applied.

BACKGROUND ART

[0002] Conventionally, conductive pastes have been widely used as amaterial forming a conductive film (a conductive circuit of a printedcircuit board, etc.), conductive adhesives used for conductive adhesionbetween electrical components (mounting of a device or the like on aconductive circuit, connection between conductive circuits, etc.), andso on.

[0003] The conductive paste is produced by blending a powderedconductive component, together with a binding agent such as resin and asolvent, in a predetermined ratio. Further, there is a conductive pastefrom which a solvent is omitted using a liquid binding agent such asliquid curable resin.

[0004] Generally employed as the conductive component are metal powdershaving an average particle diameter of approximately one to several tensof micrometers and having a granular shape, a foil shape (a scale shape,a flake shape), and so on. Examples of metals forming the metal powdersinclude Ag, Cu, Ni, Al, etc.

[0005] However, it is difficult because there is a technical limit tomake the electrical resistance of a conductive film or a conductiveadhesive portion with conductive adhesives (hereinafter genericallyreferred to as a “conductive film”) lower than that at the current levelusing such conventional metal powders.

[0006] That is, in the conductive film, a current flows through a lot ofmetal powders dispersed in the binding agent. Therefore, it isconsidered that to fill the binding agent with the metal powders with ahigh density to increase the number of contact points at which the metalpowders are directly brought into contact with one another is aneffective method of reducing the electrical resistance of the conductivefilm. Examples of specific methods thereof include one of reducing theparticle diameter of each of the metal powders.

[0007] In a general production method for metal powders, however, it isnot easy to produce metal powders on the order of sub-microns smallerthan the above-mentioned range. Moreover, even if the metal powders canbe produced, the smaller the particle diameter of each of the fine metalpowders becomes, the more easily the metal powders aggregate. Therefore,the metal powders tend to be difficult to uniformly disperse in thebinding agent.

[0008] Moreover, the respective surfaces of the actual metal powders arecovered with an oxide film or the like, and contact resistance isproduced by the oxide film or the like at each of contact points thereamong. The larger the number of contact points becomes, the higher thecontact resistance when viewed as the overall film becomes. Therefore,the electrical resistance of the conductive film also tends to beincreased.

[0009] Therefore, a method of reducing the particle diameter of each ofthe metal powders to increase the filling density thereof, to reduce theelectrical resistance of the conductive film has a technical limitation.

[0010] Furthermore, the conventional metal powders have shapes having alow aspect ratio such as a granular shape and a foil shape, as describedabove. Therefore, the conductivity of the conductive film isapproximately equal along both its thickness and its plane. That is, aconductive film having a low anisotropic conductivity can be formed.

[0011] Conversely, there is problem that a conductive film cannot beformed superior in such an anisotropic conductivity that theconductivity is high in only the thickness direction, while being low inthe other direction, for example.

[0012] In recent years, the inventors have given consideration in orderto put to practical use a plating method for applying a conductive pasteover a base to form a conductive film, then making a plated coating growon the conductive film by electroplating using the conductive film as anelectrode and a production method for a metal component having a finepattern portion on the order of sub-microns and a thickness of not morethan 100 μm (herein after referred to as a “fine metal component”)utilizing the plating method.

[0013] When the conventional conductive paste is used for the methods,however, the particle sizes of metal grains in the formed plated coatinghave a distribution discontinuously changed along the thickness of theplated coating. Therefore, it has become clear that a plated coatinghaving a uniform crystal structure cannot be obtained throughout thethickness, so that a fine metal component having good properties cannotbe produced.

[0014] When further consideration is given to the cause, the followingfacts are made clear.

[0015] That is, the conductive film formed using the conventionalconductive paste contains metal powders having an average particlediameter of not less than 1 μm, which is not so small, as compared withthe fine metal component, as described above.

[0016] When the surface of the conductive film is microscopically viewedat the size level of the fine metal component, therefore, it is notelectrically uniform because conductive portions to which the metalpowders are exposed and insulation portions there among are in a statewhere they are distributed in an irregular patch shape in conformitywith the sizes of the metal powders.

[0017] Moreover, when the surface of the conductive film is similarlymicroscopically viewed at the size level of the fine metal component, itis not flat because it has irregularities, which are not so small, ascompared with the size of the fine metal component, corresponding to thesizes of the metal powders.

[0018] The crystal structure of the plated coating by electroplating isliable to be affected by a base. When the plated coating is made to growusing as a base the conductive film whose surface is neitherelectrically uniform nor flat, as described above, the particle sizes ofthe grains produced in the plated coating partially in the early stagesof coating formation tend to be made significantly larger than theoriginal particle sizes obtained when the plated coating is made to growon the flat metal surface.

[0019] The grains of the same original particle sizes as those in a casewhere the plated coating is made to grow on the flat metal surface arenot produced until the stage in which the growth of the plated coatingprogresses so that the surface thereof comes closer to a flat metalsurface. Thereafter, the plated coating grows in the particle diameter.

[0020] Therefore, the plated coating does not have a uniform crystalstructure throughout, and has such a distribution that the particlesizes of the metal grains forming the plated coating are discontinuouslychanged in the thickness direction. Specifically, the plated coating isformed in a two-layered structure comprising an area where the particlesizes of the metal grains forming the plated coating are larger than theoriginal particle sizes and an area where they are equal to the originalparticle sizes.

[0021] Furthermore, in a production method for a fine metal component towhich the plating method is applied, a mold composed of an insulatingmaterial such as resin having a fine through-hole pattern correspondingto the shape of the fine metal component is made to adhere and fixed ona conductive substrate such as a metal plate with a conductive filmcomposed of a conductive paste intervened between the conductivesubstrate and the mold, to form a mold for electroforming.

[0022] On the surface of the conductive substrate or the conductivefilm, exposed at a portion of the through-hole pattern, in the mold forelectroforming, the plated coating is then made to selectively grow byelectroplating using the surface as an electrode, thereby forming a finemetal component corresponding to the shape of the through-hole pattern.

[0023] When the mold and the conductive substrate are removed, the finemetal component is obtained.

[0024] The conductive film may be formed on the whole surface of theconductive substrate by applying the conductive paste to the wholesurface of the conductive substrate to make the mold adhere on theconductive substrate, followed by drying and solidification. In thiscase, the plated coating is made to grow on the conductive film exposedat the portion of the through-hole pattern of the mold forelectroforming, thereby forming the fine metal component.

[0025] Furthermore, the conductive film may be formed only in anadhesive portion between the mold and the conductive substrate byapplying the conductive paste to a surface, adhering to the conductivesubstrate, of the mold to make the mold adhere on the conductivesubstrate, followed by drying and solidification. In this case, theplated coating is made to grow on the conductive substrate exposed atthe portion of the through-hole pattern of the mold for electroforming,thereby forming the fine metal component.

[0026] In the latter configuration, however, it is difficult to preventthe conductive paste from protruding into the through-hole pattern whenthe mold is made to adhere on the conductive substrate. Therefore, in aperipheral edge of the through-hole pattern of the mold forelectroforming, there occurs a state where the conductive pasteprotrudes into the through-hole pattern, followed by drying andsolidification, so that the conductive film is formed. The platedcoating also grows thereon, thereby forming the fine metal component.

[0027] In either one of the cases, therefore, the produced fine metalcomponent includes an area, where the particle sizes of the grains arelarger than the original ones, as described above, which has grown onthe conductive film, thereby making it impossible to obtain desiredphysical, mechanical or electrical properties when viewed as a whole.

[0028] Furthermore, the fine metal component has a two-layered structurecomprising an area where the particle sizes of the grains are large andthe other area where the particle sizes of the grains are equal to theoriginal ones, and the two areas differ in physical and mechanicalproperties. Accordingly, the fine metal component is liable to bedistorted depending on external conditions such as a temperature changeand is liable to be damaged depending on circumstances.

[0029] In order to remove the conductive film in the through-holepattern to expose the conductive substrate, therefore, it is consideredthat the inside of the through-hole pattern before electroplating iscleaned with a solvent (wet-etched) or dry-etched.

[0030] In either processing, however, a mold made of resin is liable tobe damaged. Particularly, an edge of the through-hole pattern isrounded, or a side wall of the through-hole pattern is gouged, so thatthe through-hole pattern is liable to be deformed. Therefore, therearises such a new problem that the shape reproducibility of the finemetal component is lowered.

DISCLOSURE OF THE INVENTION

[0031] A primary object of the present invention is to provide a newconductive paste capable of further making the electrical resistance ofa conductive film lower than that at the current level.

[0032] Another object of the present invention is to provide a newconductive film that can be used in applications which have not been sofar considered because it has an anisotropic conductivity.

[0033] Still another object of the present invention is to provide a newplating method capable of forming a plated coating having a uniformcrystal structure throughout.

[0034] A further object of the present invention is to provide a newproduction method capable of producing a fine metal component havinggood properties because it has a uniform crystal structure throughoutwith high shape reproducibility.

[0035] A conductive paste according to the present invention ischaracterized in that a metal powder having the form of fine metalparticles being linked in a chain shape is contained as a conductivecomponent.

[0036] The chain-shaped metal powder used as the conductive component inthe present invention is formed in the form of a lot of fine metalparticles on the order of sub-microns being linked in a chain shape bythe reduction and deposition method or the like, described later.Accordingly, the contact resistance between the metal particles can bemade smaller than before.

[0037] Usable as the chain-shaped metal powder is one having a structurein which a metal film is further deposited around a lot of linked metalparticles, as also described later. In such a metal powder, the metalparticles can be electrically connected to one another by the metalfilm, thereby making it possible to further reduce the contactresistance therebetween.

[0038] Moreover, the specific surface area of the chain-shaped metalpowder is larger than that of the conventional metal powders in agranular shape or the like. Accordingly, the metal powders can beuniformly dispersed in the binding agent without aggregating, forexample.

[0039] If the chain-shaped metal powder is used, therefore, a conductivefilm identical to one in which granular metal powders on the order ofsub-microns, which have been conventionally unfeasible, are dispersedwith a high density and uniformly in binding resin without increasingthe contact resistance therebetween and aggregating, for example, can beformed by the fine metal particles forming the metal powder.

[0040] According to the conductive paste in the present invention,therefore, the electrical resistance of the conductive film can be madeinfinitely lower than that at the current level.

[0041] It is preferable that the chain-shaped metal powder or each ofthe metal particles forming the metal powder is formed of

[0042] a metal having paramagnetism,

[0043] an alloy of two or more types of metals having paramagnetism,

[0044] an alloy of metal having paramagnetism and other metal, or

[0045] a complex containing metal having paramagnetism.

[0046] Examples of such a metal powder include ones having variousstructures from one in which a lot of fine metal particles are linked ina chain shape merely by a magnetic force to one in which a metal film isfurther deposited, as described above, around linked metal particles sothat the metal particles are tightly bonded to one another. In eitherone of them, the metal particles basically hold a magnetic force.

[0047] Therefore, the chain is not easily cut even by the degree of astress created in producing or applying the conductive paste to form theconductive film, for example. Moreover, if the chain is cut, the chainis recombined on the basis of a magnetic force of the metal particles atthe time point where no stress is applied, or a plurality of chains arebrought into contact with one another so that a conductive network iseasily formed.

[0048] Consequently, it is possible to further reduce the electricalresistance of the conductive film.

[0049] It is preferable that the whole or apart, having a magneticforce, of the chain-shaped metal powder or each of the metal particlesis formed by the reduction and deposition method for depositing themetal powder or each of the metal particles in a solution containing onetype or two or more types of metal ions including metal ions havingparamagnetism by reducing the ions to a metal using a reducing agent inthe solution.

[0050] When the fine metal particles on the order of sub-micronsincluding the metal having paramagnetism are deposited in the solutionby the reduction and deposition method, the metal particles are formedin a single-crystal structure or a structure close thereto. Accordingly,the metal particles are simply polarized into a bipolar phase, and areautomatically linked in a chain shape, thereby forming a chain-shapedmetal powder.

[0051] Therefore, it is easy to produce the chain-shaped metal powder,thereby making it possible to improve the production efficiency of theconductive paste and reduce the cost thereof.

[0052] The respective particle diameters of the metal particles formedby the reduction and deposition method are uniform, and the particlesize distribution is sharp. Consequently, the chain-shaped metal powderformed by linking a lot of metal particles is superior in the effect ofbringing the surface of the conductive film into an electrically uniformstate. Accordingly, the conductive paste can be suitably used for aplating method or a production method for a fine metal component,described later.

[0053] It is preferable that the reducing agent used for the reductionand deposition method is a trivalent titanium compound.

[0054] When the trivalent titanium compound such as titanium trichlorideis used as the reducing agent, the solution obtained after thechain-shaped metal powder is formed can be repeatedly regenerated to astate where it can be utilized for producing the chain-shaped metalpowder by electrolytic regeneration.

[0055] The particle diameter of each of the metal particles may be onthe order of sub-microns, as described above. Particularly in a platingmethod or a production method for a fine metal component, describedlater, however, it is preferable that the particle diameter of each ofthe metal particles is not more than 400 nm in order to form aconductive film whose surface is electrically more uniform, and is moreflat when microscopically viewed at the size level of the fine metalcomponent. For the same reason, it is preferable that the diameter ofthe chain of the metal powder is not more than 1 μm.

[0056] In a conductive paste respectively containing the chain-shapedmetal powder and a binding agent as solid contents, when the content ofthe chain-shaped metal powder in the total amount of the solid contentsis less than 5% by weight, the number of contact points among the metalparticles forming the metal powder is reduced, so that the conductivityof the conductive film may be reduced.

[0057] Conversely, when the content of the chain-shaped metal powder inthe total amount of the solid contents exceeds 95% by weight, thecontent of the binding agent is relatively insufficient. Accordingly,the effect of binding a lot of metal powders to form a strong conductivefilm by the binding agent may be insufficient.

[0058] Therefore, it is preferable that the content of the chain-shapedmetal powder in the total amount of the solid contents in the conductivepaste according to the present invention is 5 to 95% by weight.

[0059] A conductive film according to the present invention ischaracterized in that the conductive paste containing the chain-shapedmetal powder to which the magnetic force is applied, as described above,is applied over a base to form a coating film, a magnetic field isapplied to the coating film from a predetermined direction, to orient achain-shaped metal powder in the coating film in a predetermineddirection corresponding to the magnetic field, and the coating film issolidified to fix the orientation of the metal powder.

[0060] In the present invention, the orientation of the metal powderdispersed in the coating film can be fixed by solidifying the coatingfilm in a state where the metal powder is oriented, by applying themagnetic field, as described above, in a predetermined direction alongits magnetic flux. The conductive film presents such an anisotropicconductivity that the conductivity is specifically high in only thedirection in which the chain-shaped metal powder is oriented, whilebeing low in the other direction.

[0061] According to the present invention, therefore, a specialconductive film whose conductivity is high in the thickness direction, aparticular direction having a predetermined angle to the thicknessdirection, or one direction in its plane, for example, can be formed.Accordingly, the conductive film can be used in applications which havenot been so far considered.

[0062] A plating method according to the present invention ischaracterized by comprising the steps of applying the conductive pasteaccording to the present invention over a base to form a conductivefilm; and making a plated coating grow on the conductive film byelectroplating using the conductive film as an electrode.

[0063] The conductive film formed using the conductive paste accordingto the present invention has a high conductivity, as described above.

[0064] Moreover, when the surface of the conductive film ismicroscopically viewed at the size level of the fine metal component,for example, the metal particles, significantly smaller than the finemetal component, constituting the chain-shaped metal powder are almostuniformly dispersed in a state where they are electrically integrallyconnected to one another through a conductive network by mutual contactamong a lot of metal powders. Therefore, the surface of the conductivefilm is electrically uniform.

[0065] Moreover, the surface of the conductive film is nearly flatbecause it only has significantly smaller irregularities than the finemetal component, corresponding to the sizes of the metal particles.

[0066] When the plated coating is made to grow by electroplating on thesurface of the conductive film, therefore, the grains of the sameoriginal particle sizes as those in a case where it is made to grow on aflat metal surface are produced from the early stages of film formation.Accordingly, the plated coating having a uniform crystal structurethroughout can be formed.

[0067] It is preferable that the volume resistivity of the conductivefilm used for the plating method according to the present invention isnot more than 1 Ω·cm.

[0068] When the volume resistivity of the conductive film is within theabove-mentioned range, the loss of energy such as heat generation can bereduced by reducing the electrical resistance at the time ofelectroplating.

[0069] Furthermore, it is preferable that in the conductive paste usedfor the plating method according to the present invention, thechain-shaped metal powder contains at least one type of metal which isthe same as that contained in the plated coating.

[0070] According to the configuration, the plated coating can becontinuously subjected to crystal growth from the surface of thechain-shaped metal powder exposed to the surface of the conductive film.Therefore, it is easier to control the particle sizes of the grains inthe plated coating to the original ones.

[0071] A production method for a fine metal component according to thepresent invention is characterized by comprising the steps of:

[0072] fixing a mold composed of an insulating material having a finethrough-hole pattern corresponding to the shape of the fine metalcomponent on a conductive substrate with a conductive film composed of aconductive paste intervened between the conductive substrate and themold according to the present invention, to form a mold forelectroforming; and

[0073] making a plated coating selectively grow on a surface of theconductive substrate or the conductive film exposed at a portion of thethrough-hole pattern of the mold for electroforming by electroplatingusing the surface as an electrode, to form a fine metal productcorresponding to the shape of the through-hole pattern.

[0074] As described in the foregoing, the plated coating formed byelectroplating on the surface of the conductive film formed using theconductive paste according to the present invention has the same uniformcrystal structure as that directly formed on the surface of a conductivesubstrate made of metal throughout depending on the properties of thechain-shaped metal powder.

[0075] In either one of a case where the plated coating is made to growon the surface of the conductive film exposed at the portion of thethrough-hole pattern of the mold for electroforming and a case where theplated coating is made to grow on the surface of the conductivesubstrate exposed at the portion of the through-hole pattern of the moldfor electroforming and the surface of the conductive film which hasprotruded thereinto, therefore, a fine metal component having goodproperties having a single layered structure in which desired physical,mechanical, and electrical properties can be exhibited because thegrains are of the original particle sizes.

[0076] Therefore, the step of removing the conductive film to expose theconductive substrate, which may damage the mold made of resin is notrequired, thereby making it possible to also produce the fine metalcomponent faithfully to the shape of the mold with high reproducibility.

[0077] In the conductive paste, respectively containing the chain-shapedmetal powder and the binding agent as solid contents, used for theabove-mentioned production method, when the content of the chain-shapedmetal powder in the total amount of the solid contents exceeds 20% byvolume, the content of the binding agent is relatively reduced.Accordingly, the adhesive strength of the conductive paste is lowered,so that the conductive substrate and the mold which are made ofdifferent types of materials may not be firmly fixable.

[0078] Contrary to this, if the content of the chain-shaped metal powderis not more than 20% by volume, the adhesive strength of the conductivepaste is improved, thereby making it possible to more firmly fix theconductive substrate and the mold. Moreover, the conductive film formedusing the conductive paste can be maintained in a state where theresistance is lower and the conductivity is higher, as compared withthose in a case where the same amount of metal powder having anothershape such as a granular shape is used, depending on the properties ofthe chain-shaped metal powder, described above. Therefore, it ispossible to produce a fine metal component having good properties, asdescribed above.

[0079] In a case where the content is less than 0.05% by volume, thenumber of contact points among the metal particles forming the metalpowder is significantly reduced irrespective of the fact that thechain-shaped metal powder is used. Accordingly, the conductivity of theconductive film is greatly lowered, so that a fine metal componenthaving good properties may not be producible.

[0080] It is preferable that the content of the chain-shaped metalpowder in the total amount of the solid contents in the conductive pasteused for producing the fine metal component is 0.05 to 20% by volume.

[0081] The conductive film formed using the conductive paste containingthe above-mentioned percentage by volume of the chain-shaped metalpowder has a significantly high conductivity by itself depending on theproperties of the chain-shaped metal powder, as described above.

[0082] However, the smaller the content is in the above-mentioned range,the more conductive portions to which the chain-shaped metal powder isexposed are liable to enter a state where they are distributed in aso-called sea-island structure in an insulated portion composed of thebinding agent when the surface of the conductive film is microscopicallyviewed at the level of the fine metal component. Particularly, thereoccurs a case where the distribution density of power feeding points atthe start of electroplating is insufficient.

[0083] In such a case, it is preferable that used as the conductivepaste is one containing the chain-shaped metal powder as well as aspherical metal powder having a smaller particle diameter than thechain-shaped metal powder.

[0084] In such a configuration, it is possible to fill a portion betweenthe conductive portions formed by the chain-shaped metal powder of theconductive film with a granular metal powder to increase thedistribution density of the power feeding points at the start ofelectroplating. Therefore, a fine metal component having betterproperties can be produced.

[0085] It is preferable that in the conductive paste, the content of thechain-shaped metal powder in the total amount of the solid contents is0.05 to20% by volume for the same reason as described above.

[0086] In a case where the content of the granular metal powder is lessthan 0.05% by volume, the effect of filling the portion between theconductive portions formed by the metal powder of the conductive filmwith the metal powder to increase the distribution density of the powerfeeding points at the start of electroplating may be insufficient.

[0087] Therefore, the higher the content of the granular metal powderis, the more preferable it is when consideration is given to the effectof filling the portion between the conductive portions to increase thedistribution density of the power feeding points at the start ofelectroplating.

[0088] When the content of the granular metal powder exceeds 20% byvolume because the chain-shaped metal powder and the granular metalpowder are mixed in the conductive film, however, the content of thebinding agent is made relatively too low. Therefore, the adhesivestrength of the conductive paste is lowered, and the strength of theconductive film itself is lowered, so that the conductive substrate andthe mold may not be firmly fixable.

[0089] Consequently, it is preferable that the content of the granularmetal powder in the total amount of the solid contents is 0.05 to 20% byvolume.

[0090] Another production method for a fine metal component according tothe present invention is characterized by comprising the steps of:

[0091] forming on a conductive substrate a first conductive filmcomposed of the conductive paste according to the present invention anda second conductive film composed of a conductive paste containing ametal powder having a smaller particle diameter than a chain-shapedmetal powder contained in the first conductive film in this order, andfixing a mold composed of an insulating material having a finethrough-hole pattern corresponding to the shape of the fine metalcomponent on a conductive substrate with both the conductive filmsintervened between the conductive substrate and the mold, to form a moldfor electroforming; and

[0092] making a plated coating selectively grow on a surface of thesecond conductive film exposed at a portion of the through-hole patternof the mold for electroforming by electroplating using the surface as anelectrode, to form a fine metal component corresponding to the shape ofthe through-hole pattern.

[0093] According to the present invention, it is possible to fill aportion between conductive portions distributed in an island shape ofthe first conductive film with the metal powder in the second conductivefilm to increase the distribution density of power feeding points at thestart of electroplating in the same manner as described above, therebymaking it possible to produce a fine metal component having betterproperties.

[0094] When the content of the metal powder in the total amount of thesolid contents in the conductive paste which is the original form of thesecond conductive film is less than 0.05% by volume, the effect offilling the portion between the conductive portions of the firstconductive film, described above, with the metal powder having a smallparticle diameter to increase the distribution density of the powerfeeding points at the start of electroplating may be insufficient.

[0095] The higher the content of the metal powder in the conductivepaste which is the original form of the second conductive film is, themore preferable it is when consideration is given to the effect offilling the portion between the conductive portions to increase thedistribution density of the power feeding points at the start ofelectroplating. Further, the conductive paste may be one that makes thefirst conductive film and the mold both composed of the same type ofmaterial such as resin adhere to each other. Accordingly, the content ofthe binding agent can be made significantly lower than that in the caseof the first conductive film.

[0096] When the content of the metal powder exceeds 70% by volume,however, the content of the binding agent becomes relatively too low.Accordingly, the adhesive strength of the conductive paste is lowered,and the strength of the second conductive film itself is lowered, sothat the first conductive film and the mold may not be firmly fixable.

[0097] Consequently, it is preferable that the content of the metalpowder in the total amount of the solid contents in the conductive pasteforming the second conductive film is 0.05 to 70% by volume.

[0098] The [0015] column of Japanese Laid Opened Patent Publication No.JP-2001-200305-A2discloses that fine particles of an alloy havingparamagnetism having an average particle diameter of approximately 50 nmmay be linked in a chain shape to form secondary particles.

[0099] However, the gazette aims at providing an electromagnetic waveshielding material, and the electromagnetic wave shielding material musthave insulating properties, as is well-known. Therefore, the idea ofpositively utilizing secondary particles linked in a chain shape, asdescribed above, for positively improving the conductivity is notincluded at all in the gazette.

[0100] As its proof, the above-mentioned gazette discloses that the fineparticles of the alloy, together with synthetic resin, are kneaded andused as a material for injection molding to form the electromagneticwave shielding material, and the fine particles of the alloy are mixedwith sol-gel ceramics or the like to be used as a slurry for spraymolding for an electromagnetic wave shield.

[0101] In the molding methods, a greater stress which is not comparableto that in a case where the fine particles of the alloy are used as apaste is applied. Accordingly, the fine particles of the alloy cannotmaintain the shape of the secondary particles linked in a chain shape,and are dispersed in the electromagnetic wave shield in a state wherethey are broken and scattered for each of the fine particles of thealloy which are suitable for the electromagnetic wave shield.

[0102] Therefore, the description of the above-mentioned gazette neitherdiscloses nor suggests the present invention.

[0103] Furthermore, Japanese Laid Opened Patent Publication No.JP-H08-273431-A2 discloses a conductive paste using dendrite grains as aconductive component. However, the “dendrite grains” herein referred toare a solid metal powder having an aspect ratio of not more than 10, andare only one deformation of the metal powder in a granular shape or thelike described in the prior art of the present invention.

[0104] Therefore, the description of the above-mentioned gazette neitherdiscloses nor suggests the present invention.

BRIEF DESCRIPTION OF DRAWINGS

[0105]FIGS. 1A to 1F are cross-sectional views each showing an exampleof a chain-shaped metal powder contained as a conductive component in aconductive paste according to the present invention in partiallyenlarged fashion.

[0106]FIGS. 2A to 2E are cross-sectional views showing an example of thesteps of forming a mold composed of an insulating material used in aproduction method for a fine metal component according to the presentinvention.

[0107]FIGS. 3A and 3B are cross-sectional views showing an example ofthe steps of forming a mold for electroforming using the above-mentionedmold.

[0108]FIGS. 4A to 4C are cross-sectional views showing another exampleof the steps of forming a mold for electroforming using theabove-mentioned mold.

[0109]FIGS. 5A to 5D are cross-sectional views showing an example of thesteps of producing a fine metal component by a production methodaccording to the present invention using the above-mentioned mold forelectroforming.

[0110]FIGS. 6A and 6B are cross-sectional views showing still anotherexample of the steps of forming a mold for electroforming using theabove-mentioned mold.

[0111]FIGS. 7A to 7C are cross-sectional views showing a further exampleof the steps of forming a mold for electroforming using theabove-mentioned mold.

[0112]FIG. 8 is an electron micrograph showing the structure ofparticles forming a chain-shaped Ni powder produced in an example 1 ofthe present invention.

[0113]FIG. 9 is an electron micrograph showing the structure ofparticles forming a chain-shaped Permalloy powder produced in an example2 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0114] The present invention will be described.

Conductive Paste

[0115] A conductive paste according to the present invention ischaracterized in that it contains a metal powder having the form of alot of fine metal particles being linked in a chain shape as aconductive component, as described above.

[0116] (Metal Powder)

[0117] Usable as the chain-shaped metal powder is any type of metalpowders respectively produced by various types of methods such as avapor phase method and a liquid phase method and having various chainstructures such as a straight-chain structure and a branched-chainstructure.

[0118] It is preferable that the particle diameter of each of the metalparticles forming the chain-shaped metal powder is on the order ofsub-microns, and particularly not more than 400 nm. Further, it ispreferable that the diameter of the chain is not more than 1 μm. Thereasons for these are as previously described.

[0119] It is more preferable that the particle diameter of each of themetal particles is particularly not more than 200 nm in theabove-mentioned range, considering that a conductive film which iselectrically uniform and is flat is formed. When the particle diameteris too small, however, the size of the metal powder itself formed of themetal particles being linked in a chain shape is too small, so that thefunction of the metal powder as a conductive component may not besufficiently obtained. Consequently, it is preferable that the particlediameter of each of the metal particles is not less than 10 nm.

[0120] It is more preferable that the diameter of the chain isparticularly not more than 400 nm in the above-mentioned range, alsoconsidering that a conductive film which is electrically uniform and isflat is formed. When the diameter of the chain is too small, however,the chain may be easily cut even by the degree of a stress created inproducing or applying the conductive paste. Consequently, it ispreferable that the diameter of the chain is not less than 10 nm.

[0121] It is preferable that as the above-mentioned chain-shaped metalpowder, the metal powder or each of the metal particles forming themetal powder is formed of a metal having paramagnetism, an alloy of twoor more types of metals having paramagnetism, an alloy of metal havingparamagnetism and other metal, or a complex containing metal havingparamagnetism. The reason for this is as previously described.

[0122] Specific examples of the metal powder containing the metal havingparamagnetism include any one of the following types of metal powders(a) to (f) or a mixture of two or more types of metal powders.

[0123] (a) A metal powder M1 obtained by linking a lot of metalparticles m1 on the order of sub-microns, formed of a metal havingparamagnetism, an alloy of two or more types of metals havingparamagnetism, or an alloy of metal having paramagnetism and othermetal, in a chain shape by its own magnetism, as illustrated inpartially enlarged fashion in FIG. 1A.

[0124] (b) A metal powder M2 obtained by further depositing a metallayer m2 composed of a metal having paramagnetism, an alloy of two ormore types of metals having paramagnetism, or an alloy of metal havingparamagnetism and other metal on the surface of the metal powder M1 inthe foregoing item (a), to tightly bond the metal particles to oneanother, as illustrated in partially enlarged fashion in FIG. 1B.

[0125] (c) A metal powder M3 obtained by further depositing a metallayer m3 composed of another metal such as Ag, Cu, Al, Au, or Rh or analloy on the surface of the metal powder M1 in the foregoing item (a),to tightly bond the metal particles to one another, as illustrated inpartially enlarged fashion in FIG. 1C.

[0126] (d) A metal powder M4 obtained by further depositing a metallayer m4 composed of another metal such as Ag, Cu, Al, Au, or Rh or analloy on the surface of the metal powder M2 in the foregoing item (b),to tightly bond the metal particles to one another, as illustrated inpartially enlarged fashion in FIG. 1D.

[0127] (e) A metal powder M5 obtained by coating the surface of agranular core material m5 a formed of a metal having paramagnetism, analloy of two or more types of metals having paramagnetism, or an alloyof metal having paramagnetism and other metal with a coating layer m5 bcomposed of other metal such as Ag, Cu, Al, Au, or Rh or an alloy toobtain a complex m5, and linking a lot of complexes m5 in a chain shapeas metal particles by the magnetism of the core material m5 a, asillustrated in partially enlarged fashion in FIG. 1E. (f) A metal powderM6 obtained by further depositing a metal layer m6 composed of anothermetal such as Ag, Cu, Al, Au, or Rh or an alloy on the surface of themetal powder M5 in the foregoing item (e), to tightly bond the metalparticles to one another, as illustrated in partially enlarged fashionin FIG. 1F.

[0128] Although in the drawings, the metal layers m2, m3, m4, and m6 andthe coating layer m5 are respectively described as single layers, eachof the layers may have a laminated structure of two or more layerscomposed of the same metal material or different metal materials.

[0129] Furthermore, it is preferable that the whole of the metal powderor each of the metal particles formed of a metal having paramagnetism,an alloy of two or more types of metals having paramagnetism, or analloy of metal having paramagnetism and other metal out of the foregoingmetal powders, or

[0130] a portion containing metal having paramagnetism of the metalpowder or each of the metal particles formed of a complex containing themetal having paramagnetism

[0131] is formed by being deposited in a solution containing ionsforming metal having paramagnetism which is its forming material byadding a reducing agent to the solution by the reduction and depositionmethod, as described above.

[0132] In the reduction and deposition method, ammonia water or the likeis added to a solution in which a trivalent titanium compound such astitanium trichloride as a reducing agent and sodium citrate or the likeare dissolved (hereinafter referred to as a “reducing agent solution”)to adjust the pH thereof to 9 to 10. Consequently, trivalent titaniumions are bonded to a citric acid serving as a complexing agent to form acoordination compound, so that activation energy in the case ofoxidation from Ti (III) to Ti (IV) is lowered, and a reduction potentialis raised. Specifically, a potential difference between Ti (III) and Ti(IV) exceeds 1V. This value is a significantly higher value, as comparedwith a reduction potential from Ni (II) to Ni (0) and a reductionpotential from Fe (II) to Fe (0). Accordingly, it is possible toefficiently reduce ions forming various types of metals, to deposit andform metal particles, metal films, and so on.

[0133] A solution containing ions forming a metal having paramagnetismsuch as Ni or a solution containing two or more types of ions forming analloy containing a metal having paramagnetism is then added to theabove-mentioned reducing agent solution.

[0134] Consequently, Ti (III) functions as a reducing agent, to reducemetal ions and deposit the reduced metal ions in the solution whenitself is oxidized to Ti (IV). That is, metal particles composed of theabove-mentioned metal or alloy are deposited in the solution, and a lotof metal particles are linked in a chain shape by their own magnetism,to form a chain-shaped metal powder. When the deposition is furthercontinued after that, a metal layer is further deposited on the surfaceof the metal powder, thereby tightly bonding the metal particles.

[0135] That is, the metal powders M1 and M2 in the foregoing items (a)and (b) and the metal particles m1 which are the original form of themetal powders, the core materials m5 a in the complexes m5 which are theoriginal form of the metal powders M5 and M6 in the foregoing items (e)and (f), or the like are produced by the above-mentioned method.

[0136] Furthermore, the respective particle diameters of the metalparticles m1 or the core materials m5 a are uniform, and the particlesize distribution is sharp. The reason for this is that reductionreaction uniformly progresses in the reaction system. Consequently, anyof the metal powders M1 to M6 produced from the metal particles m1 orthe core materials m5 a is superior in the effect of bringing thesurface of the conductive film into an electrically uniform state, andcan be suitably employed for a plating method and a production methodfor a fine metal component.

[0137] The reducing agent solution obtained after the metal particles,the core materials, or the like are deposited can be utilized forproducing the chain-shaped metal powder by the reduction and depositionmethod repeatedly any number of times by performing electrolyticregeneration, as described above. That is, if the reducing agentsolution obtained after the metal particles, the core materials, or thelike are deposited is put in an electrolytic cell, for example, toreduce Ti (IV) to Ti (III) by applying a voltage, it can be employed asa reducing agent solution for electrolytic deposition. This is becausetitanium ions are hardly consumed at the time of electrolyticdeposition, that is, titanium ions, together with a metal to bedeposited, are not deposited.

[0138] Examples of a metal or an alloy having paramagnetism forming themetal particles, the core materials, or the like include metals Ni, Fe,and Co, an alloy of two or more types of ones of the metals, forexample. Particularly, Ni, a Ni-Fe alloy (Permalloy), and so on aresuitably employed. Particularly metal particles formed of such a metalor alloy are strong in magnetic interaction in a case where they arelinked in a chain shape and therefore, are superior in the effect ofreducing contact resistance between the metal particles.

[0139] Examples of other metals, together with the metal or alloy havingparamagnetism, forming the complexes in the foregoing items (c), (d),(e), and (f) include Ag, Cu, Al, Au, and Rh. Particularly Ag is suitablyused because the conductivity thereof is high.

[0140] A portion formed of the other metal, described above, in thecomplex can be formed by various types of film forming methods such asan electroless plating method, an electrolytic plating method, areduction and deposition method, and a vacuum evaporation method.

[0141] (Binding Agent)

[0142] Usable as a binding agent, together with the chain-shaped metalpowder, forming the conductive paste is any of various types ofcompounds conventionally known as a binding agent for a conductivepaste. Examples of such a binding agent include thermoplastic resin,curable resin, and liquid curable resin. Particularly preferableexamples include acrylic resin, fluorocarbon resin, and phenolic resin.

[0143] (Conductive Paste) The conductive paste is produced by blendingthe chain-shaped metal powder and the binding agent, together with asuitable solvent, in a predetermined ratio. Further, the solvent may beomitted using a liquid binding agent such as liquid curable resin, asdescribed above.

[0144] Although the ratio of the foregoing components is notparticularly limited, the ratio of the chain-shaped metal powder in thetotal amount of solid contents, i.e., the metal powder and the bindingagent is preferably 5 to 95% by weight. The reason for this is asdescribed above.

[0145] The conductive paste makes it possible to form a conductive filmor the like having a conductivity higher than before depending on theproperties of the chain-shaped metal powder, as described above.

[0146] That is, when the ratio of the chain-shaped metal powder is setto not less than 50% by weight which is the same as that of a normalconductive paste in the foregoing range, a conductive film or the likehaving a higher conductivity, which cannot be so for obtained, having avolume resistivity of not more than 1 Ω·cm can be formed.

[0147] In this case, the more suitable range of the ratio of thechain-shaped metal powder is 50 to 90% by weight, and the volumeresistivity of a conductive film formed in this case is approximately1×10⁻⁴˜1 Ω·cm.

[0148] The conductive paste according to the present invention makes itpossible to also form a conductive film or the like having approximatelythe same conductivity as the conventional one by making the ratio of thechain-shaped metal powder lower than before depending on the propertiesthereof.

[0149] That is, even if the ratio of the chain-shaped metal powder isset to less than 50% by weight, a conductive film or the like havingapproximately the same conductivity as the conventional one can beformed depending on the properties of the chain-shaped metal powder,thereby making it possible to achieve resource saving and costreduction.

[0150] The more suitable range of the ratio of the chain-shaped metalpowder in this case is not less than 30% by weight and less than 50% byweight, and the volume resistivity of a conductive film formed in thiscase is not more than nearly 100 Ω·cm, although it exceeds 1 Ω·cm.

Conductive Film

[0151] In order to form the conductive film according to the presentinvention in which the orientation of the chain-shaped metal powder iscontrolled, as described above, a conductive paste using as thechain-shaped metal powder a metal powder containing a metal havingparamagnetism is applied over a base to form a coating film.

[0152] By then applying a magnetic field to the coating film from apredetermined direction, the chain-shaped metal powder in the film isoriented in a predetermined direction corresponding to the magneticfield. That is, the chain-shaped metal powder is oriented, when themagnetic field is applied thereto, in the direction of its magneticflux.

[0153] When the coating film is dried, solidified, or cured when itcontains curable resin, to fix the metal powder in this state, aconductive film having such an anisotropic conductivity that theconductivity is specifically high in only the direction in which thechain-shaped metal powder is oriented, while being low in the otherdirection is formed.

[0154] A conductive film having a high conductivity in only onedirection in its plane, for example, can be suitably used as anelectrode in a plating method and a production method for a fine metalcomponent, subsequently described.

[0155] A conductive film having a high conductivity in only the otherdirection may be usable in various types of applications which have notbeen so for considered.

[0156] It is preferable that the strength of the magnetic field appliedto the coating film in order to orient the chain-shaped metal powder isnot less than nearly 7.9 A/m. In a case where the strength of themagnetic field is less than this range, the orientation of thechain-shaped metal powder maybe insufficient.

Plating Method

[0157] In a plating method according to the present invention, aconductive paste containing a chain-shaped metal powder is applied to abase to form a conductive film, followed by electroplating using theconductive film as an electrode. That is, the conductive film as acathode and a metal to be plated or platinum or the like as an anode aredipped in an electroplating bath, followed by application of a voltage,thereby making it possible to from a plated coating having a uniformcrystal structure throughout its thickness, as described above.

[0158] In this case, it is preferable that the volume resistivity of theconductive film is adjusted to not more than 1 Ω·cm. The reason for thisis as previously described. In order to adjust the volume resistivity ofthe conductive film in the above-mentioned range, the ratio of thechain-shaped metal powder to the total amount of the solid contents inthe conductive paste may be increased.

[0159] It is preferable that used as the chain-shaped metal powder inthe conductive paste is one containing at least one type of metal whichis the same as that contained in the plated coating. The reason for thisis as previously described.

[0160] Furthermore, a method of orienting the chain-shaped metal powderin only one direction in the plane of the conductive film, as describedin the previous section, is effective. In this method, the volumeresistivity in the same direction of the conductive film can be adjustedin the above-mentioned range without increasing the ratio of thechain-shaped metal powder. A conductive terminal for connection to apower supply is attached to a portion at an end in the direction of theorientation of the conductive film, for example, thereby making itpossible to perform good plating having no loss of energy.

[0161] If both the methods are combined with each other, the volumeresistivity of the conductive film can be further reduced. When theratio of the chain-shaped metal powder is set to not less than 50% byweight, and the chain-shaped metal powder is oriented in only onedirection in its plane, the volume resistivity in the same direction ofthe conductive film can be also set to less than 1×10⁻⁴ Ω·cm.

[0162] The lower limit of the volume resistivity of the conductive filmis not particularly limited. The lower limit can be employed withoutproblems until a limit value feasible by the methods described above.

Production Method (i) for Fine Metal Component

[0163] In a production method (i) for a fine metal component, a mold 3composed of an insulating material having a fine through-hole pattern 3a corresponding to the shape of the fine metal component is formed, asshown in FIG. 2D.

[0164] Although the mold 3 can be formed by various types of methods, itis preferably formed particularly by injection molding, reactiveinjection molding, or the like using a mother die produced bylithography and electroplating. Further, suitably employed as thelithography is X-ray lithography for irradiating X-rays such as SR(Synchrotron Radiation) light onto a resist and forming a fine patternby development after the irradiation.

[0165] Specifically, after a mother die IM1 which is the original formof the fine metal component is formed on a conductive substrate IM2, asshown in FIG. 2A, utilizing X-ray lithography and electroplating, aprecursor 3′ of the mold 3 having a fine recess 3 b which is theoriginal form of the through-hole pattern 3 a corresponding to the shapeof the mother die IM1 is obtained by injection molding or reactiveinjection molding (FIGS. 2B and 2C).

[0166] When the precursor 3′ is polished to penetrate through the recess3 b, the mold 3 having the through-hole pattern 3 a corresponding to theshape of the mother die IM1 is formed, as shown in FIG. 2D.

[0167] According to the method, the molds 3 can be formed in largenumbers using one mother die IM1 any number of times. As a result, theproduction cost of the fine metal component can be made significantlylower than before.

[0168] In the present invention, a conductive paste 1′ is then appliedover the whole surface of a conductive substrate 2 such as a metalplate, and the mold 3 is then superimposed thereon, as shown in FIGS. 3Aand 3B. A conductive film 1 is formed by drying the conductive paste 1′,and curing, when a binding agent is curable resin, the binding agent,and the mold 3 is fixed on the conductive substrate 2, therebymanufacturing a mold for electroforming EM.

[0169] Alternatively, a conductive paste 1′ is applied over the wholesurface of a conductive substrate 2 such as a metal plate, and theprecursor 3′ of the mold 3 obtained in FIG. 2C is superimposed thereonwith the recess 3 b positioned on the lower side, as shown in FIGS. 4Ato 4C. A conductive film 1 is formed by drying the conductive paste 1′,and curing, when a binding agent is curable resin, the binding agent,and the precursor 3′ is fixed on the conductive substrate 2 and is thenpolished to penetrate through the recess 3 b, thereby making it possibleto manufacture the same mold for electroforming EM.

[0170] In the mold for electroforming EM manufactured by the steps, thewhole surface at the bottom of the through-hole pattern 3 a is coveredwith the conductive film 1 having superior properties, as describedabove, thereby making it possible to produce a fine metal componenthaving good properties without removing the conductive film 1.

[0171] The mold for electroforming EM may be manufactured by applyingthe conductive paste to the lower surface of the mold 3, followed bydrying with the conductive paste superimposed on the conductivesubstrate 2, and curing, when the binding agent is curable resin, thebinding agent, which is not illustrated. Alternatively, the mold forelectroforming EM may be manufactured by applying the conductive pasteto the lower surface of the precursor 3′ with the recess 3 b positionedon the lower side, followed by drying with the conductive pastesuperimposed on the conductive substrate 2, curing, when the bindingagent is curable resin, the binding agent, and polishing the precursor3′ to penetrate through the recess 3 b, which is not similarlyillustrated.

[0172] In these cases, there occurs a state where the conductivesubstrate 2 is basically exposed at the bottom of the through-holepattern 3 a, as previously described, and the conductive film composedof the conductive paste which has protruded is formed particularly in apart of the peripheral edge of the through-hole pattern 3 a. However,the conductive film has superior properties, as described above, so thatit need not be removed. In this case, therefore, a fine metal componenthaving good properties can be also produced without removing theconductive film.

[0173] Suitably used as the conductive paste 1′ which is the originalform of the conductive film 1 is one which respectively contains achain-shaped metal powder and a binding agent as solid contents and inwhich the ratio of the chain-shaped metal powder to the total amount ofthe solid contents is adjusted to 0.05 to 20% by volume. The reason forthis is as described above.

[0174] Examples of the chain-shaped metal powder and the binding agentare the same ones as described above.

[0175] It is preferable that the coating thickness of the conductivepaste 1′ is 0.5 to 70 μm.

[0176] In a case where the coating thickness is less than 0.5 μm, theeffect of fixing the mold 3 on the conductive substrate 2 with theconductive paste cannot be sufficiently obtained, and the mold is easilyshifted, for example, at the time of electroplating, so that the shapereproducibility of the fine metal component may be lowered.

[0177] Conversely, in a case where the coating thickness exceeds 70 μm,when the mold 3 is superimposed on the conductive substrate 2, theexcessive conductive paste extruded by a stress created in the case ofthe superimposition, the weight of the mold 3, and so on protrude inlarge amounts into the through-hole pattern 3 a to wave and rise in adroplet shape, resulting in possibilities that a plating startingsurface is irregular in shape so that a plated coating having a uniformcrystal structure cannot be formed, and the plated coating is thinned bythe amount of the rise of the conductive paste, so that the fine metalcomponent having a predetermined thickness cannot be produced.

[0178] Examples of the conductive substrate 2 include a substrate madeof a metal such as a stainless steel, Al, Cu or these alloy, or acomplex formed by laminating conductive layers on a nonconductivesubstrate made of Si, glass, ceramics, plastic, or the like. Conductivelayers composed of the same type or another type of metal can be alsolaminated by the sputtering method or the like, as required, on thesubstrate made of the metal or the alloy.

[0179] Suitably used as an insulating material forming the mold 3 isresin capable of injection molding, reactive injection molding, or thelike, as described above. Examples of such resin include polymethylmethacrylate, polypropylene, polycarbonate, and epoxy resin.

[0180] In the present invention, on a surface of the conductive film 1exposed at portions of the through-hole pattern 3 a, as shown in FIG.5A, or a surface of the conductive substrate 2 exposed at portions ofthe through-hole pattern 3 a and a surface of the conductive film 1composed of the conductive paste which has protruded thereinto, whichare not illustrated, of the mold for electroforming EM manufactured inthe above-mentioned manner, a plated coating is made to selectively growby electroplating using the portions as electrodes.

[0181] That is, the conductive film 1 and/or the conductive substrate 2as a cathode and a metal to be plated or platinum or the like as ananode are dipped in an electroplating bath, followed by application of avoltage, to make a plated coating grow. Consequently, a plated coating4′ which is the original form of the fine metal component, correspondingto the shape of the through-hole pattern 3 a, having a uniform crystalstructure throughout, as described above, is formed (FIG. 5B).

[0182] After the formed plated coating 4′, together with the mold 3, isthen polished or ground, for example, to line up the plated coating 4′and the mold 3 with each other to a predetermined thickness, the mold 3is removed (FIG. 5C).

[0183] Preferable as a method of removing the mold 3 is a methodperformed by non-contact such as ashing using oxygen plasma, ordecomposition by irradiation with X-rays or ultraviolet rays, forexample, in order not to deform the plated coating 4′ by application ofan excessive stress.

[0184] Finally, when the conductive film 1 and the conductive substrate2 are removed, a fine metal component 4 is completed (FIG. 5D).

[0185] Preferable as a method of removing the conductive film 1 and theconductive substrate 2 is a method of dissolving the conductive film 1using a suitable solvent or decomposing and removing the conductive film1 by dry etching or the like. Consequently, the remaining conductivesubstrate 2 maybe removed after the conductive film 1 is made todisappear.

Production Method (ii) for Fine Metal Component

[0186] In a production method (ii) for a fine metal component in thepresent invention, a mold for electroforming EM, having such a form thata mold 3 composed of an insulating material is fixed, having a finethrough-hole pattern 3 a corresponding to the shape of the fine metalcomponent, on a conductive substrate 2 with a conductive film 1intervened between the conductive substrate and the mold ismanufactured, as shown in FIG. 5A, in the same manner as the productionmethod (i) except that a conductive paste containing a chain-shapedmetal powder and a granular metal powder having a smaller particlediameter than that of the chain-shaped metal powder is used.

[0187] The specific steps are the same as those in the case of theproduction method (i).

[0188] Specifically, the mold for electroforming EM is manufactured byany of the following methods:

[0189] (A) A method of applying a conductive paste 1′ over the wholesurface of the conductive substrate 2, then superimposing the mold 3thereon, and drying, solidifying, or curing the conductive paste 1′, toform the conductive film 1 as well as to fix the mold 3 on theconductive substrate 2, as shown in FIGS. 3A and 3B.

[0190] (B) A method of applying a conductive paste to the lower surfaceof the mold 3, and then drying, solidifying, or curing the conductivepaste in a state where the conductive paste is superimposed on theconductive substrate 2, to fix the mold 3 on the conductive substrate 2,which is not illustrated.

[0191] (C) A method of applying a conductive paste 1′ over the wholesurface of the conductive substrate 2, then superimposing a precursor 3′of the mold 3 thereon with a recess 3 b positioned on the lower side,and drying, solidifying, or curing the conductive paste, to join, fix,and then polish the precursor 3′ to penetrate through the recess 3 b, asshown in FIGS. 4A and 4C.

[0192] (D) A method of applying a conductive paste to the lower surfaceof a precursor 3′ with a recess 3 b positioned on the lower side, anddrying, solidifying, or curing the conductive paste in a state where theconductive paste is superimposed on the conductive substrate 2, to join,fix, and then polish the precursor 3′ to penetrate through the recess 3b, which is not illustrated.

[0193] In the case of the methods (A) and (C), there occurs a statewhere in the mold for electroforming EM, the whole surface at the bottomof the through-hole pattern 3 a is covered with the conductive film 1.On the other hand, in the case of the methods (B) and (D), there occursa state where the conductive substrate 2 is basically exposed at thebottom of the through-hole pattern 3 a, and the conductive film composedof the conductive paste which has protruded is formed particularly in apart of a peripheral edge of the through-hole pattern 3 a.

[0194] In either one of the states, the conductive film 1 has a goodconductivity obtained by the properties of the chain-shaped metalpowder, and the distribution density of power feeding points can beincreased by the function of the granular metal powder added thereto.

[0195] Therefore, the fine metal component 4 having good properties canbe produced by subsequently carrying out the steps shown in FIGS. 5B to5D.

[0196] It is preferable that the coating thickness of the conductivepaste 1′ which is the original form of the conductive film 1 is 0.5 to70 μm for the same reason as described above.

[0197] Suitably used as the conductive paste 1′ is one whichrespectively contains a chain-shaped metal powder and a granular metalpowder as solid contents and in which the content of the chain-shapedmetal powder in the total amount of the solid contents is 0.05 to 20% byvolume, and the content of the granular metal powder therein is 0.05 to20% by volume. The reason for this is as described above.

[0198] Usable as the chain-shaped metal powder and the binding agent arethe same ones as described above.

[0199] The granular metal powder can be produced by the reduction anddeposition method, as in the foregoing.

[0200] If a metal powder is produced by a metal having no paramagnetismsuch as Ag, Cu, Al, Au, or Rh which is not linked in a chain shape bythe above-mentioned mechanism when the reduction and deposition methodis carried out, the metal powder itself presents a granular shape.

[0201] If the pH of the reducing agent solution is set to not more than7 to carry out the reduction and deposition method, a metal powdercomposed of a metal having paramagnetism can be prevented from beingformed in a chain shape and therefore, can be formed in a granularshape. That is, when the pH is set to not more than 7 to carry out thereduction and deposition method, the growth speed of the metal isrestrained. Accordingly, a metal powder having a single-crystalstructure which is easily formed in a chain shape can be prevented frombeing produced in large amounts in a solution in the early stages ofreaction. Therefore, the metal powder composed of the metal havingparamagnetism can be formed in a granular shape.

[0202] Moreover, in the granular metal powder formed by the reductionand deposition method, the particle sizes of grains are uniform, and theparticle size distribution is sharp. The reason for this is thatreduction reaction uniformly progresses in the reaction system.According to such a metal powder, therefore, the conductivity of theconductive film can be made more uniform, thereby making it possible toproduce a fine metal component having better properties.

[0203] When the metal powder is a Cu powder, it is preferable that theCu powder is formed by reducing the pH of a solution containing Cu (I)ammine complex ions to deposit a metal Cu in the shape of ultrafineparticles.

[0204] This method utilizes the fact that a Cu (I) ammine complex whichis stable in a state where a solution is basic is destabilized when thesolution is made acidic, so that Cu (I) ions (Cu¹⁺) in the complex isdisproportionated and decomposed into Cu (II) ions (Cu²⁺) and a metal Cu(Cu) and as a consequence, the metal Cu is deposited in the solution.

[0205] According to this method, the Cu powder can be produced moresafely without using both hydrazine and a hydrazine compound which aredangerous objects, which are used as a reducing agent in the reductionand deposition method. Consequently, the necessity of productionfacilities, storage facilities, and so on which are subjected to strictsafety management is eliminated.

[0206] Although a solution containing Cu (I) ammine complex ions isproduced by adding a metal Cu to a solution containing Cu (II) sulfate,ammonia, and ammonia sulfate, for example, followed by reaction underoxygen-free conditions, a solution containing Cu (II) ions obtainedafter the metal Cu is deposited to obtain a Cu powder in the subsequentstep can be reused as a starting raw material in producing a solutioncontaining Cu (I) ammine complex ions again. That is, the solution canbe used almost semipermanently.

[0207] Consequently, the production cost of the Cu powder can be madelower than before.

[0208] In all the steps from the step of preparing the solutioncontaining Cu (I) ammine complex ions, to the step of depositing themetal Cu to produce the Cu powder, described above, a componentcontaining an element which may be eutectoid with Cu, such as phosphate,need not be added. Moreover, the higher the deposition rate of the metalCu is made by adjusting the conditions of disproportionation anddecomposition reaction, the more greatly the amount of mixing ofimpurities can be reduced.

[0209] Even if a low-purity and low-cost metal Cu, such as recycle Cu,is used for preparing the solution containing Cu (I) ammine complexions, for example, therefore, the Cu powder can be maintained at highpurity.

[0210] The above-mentioned disproportionation and decomposition reactionis performed under agitation, for example, so that the deposition of themetal Cu can be almost uniformly conducted in the solution. In theproduced Cu powder, therefore, the particle diameters of a plurality ofparticles forming the produced Cu powder are almost uniform.

[0211] Moreover, when the disproportionation and decomposition reactionis performed under agitation, the metal Cu can be prevented from beingselectively deposited in only a particular portion of each of theparticles to average the growth of the particles throughout alldirections. In the produced Cu powder, therefore, the shape thereof isan almost uniform spherical shape.

[0212] If the above-mentioned Cu powder is used, therefore, theconductivity of the conductive film is further made uniform, and thesmoothness of its surface can be further improved. Therefore, a finemetal component having better properties can be produced.

Production Method (iii) for Fine Metal Component

[0213] In a production method (iii) for a fine metal component accordingto the present invention, a conductive paste is applied over the wholesurface of a conductive substrate 2 to form a first conductive film 1,and a conductive paste 5′ containing a metal powder having a smallerparticle diameter than that of a chain-shaped metal powder contained inthe first conductive film 1 is applied thereon, as shown in FIG. 6A, anda mold 3 is then superimposed thereon, as shown in FIG. 6B.

[0214] A mold for electroforming EM is manufactured by drying theconductive paste 5′ and curing, when a binding agent is curable resin,the binding agent to form a second conductive film 5 as well as to fixthe mold 3 on the conductive substrate 2.

[0215] Alternatively, the mold for electroforming EM may be manufacturedby applying the above-mentioned conductive paste 5′ over the firstconductive film 1, then superimposing a precursor 3′ of a mold 3 thereonwith a recess 3 b positioned on the lower side, drying, solidifying, orcuring the conductive paste 5′ to form a second conductive film 5 aswell as to join and fix the precursor 3′, and then polishing theprecursor 3′ to penetrate through the recess 3 b, as shown in FIGS. 7Ato 7C.

[0216] In either one of the cases, in the mold for electroforming EM,the whole surface at the bottom of a through-hole pattern 3 a is coveredwith the second conductive film.

[0217] Even if the distribution density of power feeding points at thestart of electroplating is insufficient on the surface of the firstconductive film 1, therefore, clearances there among are filled with themetal powder in the second conductive film, thereby making it possibleto increase the distribution density of the power feeding points.

[0218] Therefore, the steps shown in FIGS. 5A to 5D are subsequentlycarried out, thereby making it possible to produce a fine metalcomponent 4 having good properties.

[0219] Usable as a conductive paste 1′ which is the original form of thefirst conductive film 1 is the same one as that used in the productionmethod (i).

[0220] It is preferable that the coating thickness of the conductivepaste 1′ is 0.5 to 70 μm for the same reason as described above.

[0221] On the other hand, it is preferable that the coating thickness ofthe conductive paste 5′ which is the original form of the secondconductive film 5 is 0.5 to 70 μm.

[0222] In a case where the coating thickness is less than 0.5 μm, theeffect of fixing the mold 3 on the conductive substrate 2 with theconductive paste 5′ cannot be sufficiently obtained, and the mold may beshifted at the time of electroplating, so that the shape reproducibilityof the fine metal component may be lowered.

[0223] Conversely, in a case where the coating thickness exceeds 70 μm,when the mold 3 is superimposed on the conductive substrate 2, theexcessive conductive paste extruded by a stress created in the case ofthe superimposition, the weight of the mold 3, or the like protrudes inlarge amounts into the through-hole pattern 3 a to wave and rise in adroplet shape, resulting in possibilities that a plating startingsurface becomes irregular in shape so that a plated coating having auniform crystal structure cannot be formed, and the plated coating isthinned by the amount of the rise of the conductive paste so that a finemetal component having a predetermined thickness cannot be produced.

[0224] Suitably used as the conductive paste 5′ which is the originalform of the second conductive film 5 is one which respectively containsa metal powder having a smaller particle diameter than that ofchain-shaped metal powder included in the first conductive film 1 and abinding agent as solid contents and in which the ratio of the metalpowder to the total amount of the solid contents is adjusted to 0.05 to70% by volume. The reason for this is as described above.

[0225] Usable as the binding agent is the same one as described above.

[0226] Although the range of the particle diameter of the metal powderis not particularly limited, provided that the particle diameter issmaller than that of the chain-shaped metal powder included in the firstconductive film, the average particle diameter is preferably not morethan 400 nm. When the average particle diameter is not more than 400 nm,the number of contact points among metal particles forming the metalpowder can be increased by raising the bulk density. Accordingly, theeffect of increasing the distribution density of power feeding points bythe metal powder in the second conductive film can be further improved.

[0227] Usable as the metal powder are metal powders composed of Ag, Cu,Ni, Al, Au, Rh, etc. and having various types of shapes such as a chainshape, a granular shape, and a foil shape having a smaller particlediameter than that of the chain-shaped metal powder included in thefirst conductive film.

[0228] The chain-shaped metal powder out of the metal powders can beproduced in the same manner as described above.

[0229] The granular metal powder can be also produced in the same manneras described above.

[0230] Preferably used as the granular metal powder is one formed byreducing the pH of the solution containing cu (I) ammine complex ions,previously described to deposit the metal Cu in the shape of ultrafineparticles. If such a Cu powder is used, the conductivity of the secondconductive film is made more uniform, and the smoothness of its surfacecan be further improved, thereby making it possible to produce a finemetal component having better properties.

[0231] Any of the fine metal components produced in the productionmethods (i) to (iii) has a single layered structure capable ofexhibiting desired physical, mechanical, and electrical propertiesbecause the grains are of the original particle sizes, as previouslydescribed, and has good properties.

[0232] Examples of such a fine metal component are a contact probe usedfor a semiconductor inspection device or the like, a micro actuator usedfor an acceleration sensor or the like, a light switch, and a microconnector, etc.

Industrial Applicability

[0233] As described in the foregoing, the conductive paste according tothe present invention is useful as a material for forming a conductivefilm, conductive adhesives, etc. because the electrical resistance ofthe conductive film can be made lower than that at the current level.Further, the conductive film according to the present invention can beused in applications which have not been so far considered because ithas a unique anisotropic conductivity. The plating method according tothe present invention and the production method for a fine metalcomponent to which the plating method is applied are suitable for theproduction of a fine metal component having good properties which havenot been so far considered.

EXAMPLES

[0234] The present invention will be described on the basis examples andcomparative examples.

Example 1 Production of Chain-shaped Ni Powder

[0235] Titanium trichloride and sodium citrate were added to pure water,to prepare a reducing agent solution in which the concentrations of boththe components take values shown in the following Table 1: TABLE 1Concentration Component (mol/L) Titanium trichloride 0.102 Sodiumcitrate 0.306

[0236] Ammonia water was then added to the reducing agent solution, toadjust the pH of the reducing agent solution to 9 to 10 whilemaintaining the liquid temperature thereof at 35° C.

[0237] Furthermore, a nickel chloride hexahydrate was added to the purewater, to prepare a solution in which the concentration of nickelchloride is 0.04 mol/L.

[0238] After 100 ml of the solution was added to 100 ml of the reducingagent solution, previously described, followed by agitation at atemperature of 35° C. for one hour, a solid content deposited in thesolution was filtered, rinsed, and then dried, to produce a Ni powder.

[0239] When the shape of the obtained Ni powder was observed using ascanning-type electron microphotograph, it was confirmed that the Nipowder had the form of fine metal particles being linked in a chainshape, as shown in FIG. 8.

[0240] When the particle diameter of each of the metal particles and thediameter of the chain of the Ni powder were measured from theabove-mentioned electron microphotograph, the particle diameter of eachof the metal particles was approximately 100 nm, and the diameter of thechain was approximately 200 nm.

Preparation of Conductive Paste

[0241] 90 parts by weight of the chain-shaped Ni powder produced in theforegoing and 10 parts by weight of poly (vinylidene fluoride) servingas a binding agent, together with N-methyl-2-pyrrolidone serving as asolvent, were mixed, to prepare a conductive paste.

Formation of Conductive Film

[0242] The conductive paste prepared in the foregoing was applied to onesurface of a polyimide film serving as a base such that the amount ofadhesion of the solid content would be 20 mg/cm², and was then dried at100° C. for four hours to remove the solvent, thereby forming aconductive film.

[0243] When the surface of the conductive film was observed by a metalmicroscope, it was confirmed that there were few irregularities on thesurface so that the surface was nearly flat. The state of the surfacewas estimated to be good. When the volume resistivity of the conductivefilm was measured, it was 1×10⁻⁴ Ω·cm.

Formation of Plated Coating

[0244] A conductive terminal was then attached to the conductive film toserve as a power feeding portion, and the conductive film was dipped ina Ni plating bath prescribed as shown in the following Table 2, toperform electroplating for one hour under conditions of a currentdensity of 10 to 150 mA/cm² and a liquid temperature of 40 to 60° C.TABLE 2 Ni plating bath (pH3.5˜4.5) Component Concentration Nickelsulfamate 450 g/L Boric acid  30 g/L

[0245] After electroplating, the cross section of the plated coatingformed on the conductive film was observed using the metal microscope,to measure the sizes of grains at positions 5% above and below the crosssection of the plated coating along its thickness. When the ratio R_(ø)of the sizes of the grains was found by the following equation (1) fromthe sizes ø₁ of the grains on the side of the conductive film and thesizes ø₂ of the grains on the side of the surface of the plated coating,it was 1.1:

R_(ø)=ø₁/ø₂  (1)

[0246] Accordingly, the sizes of the grains hardly varied. It wasconfirmed that the plated coating had a uniform crystal structurethroughout the thickness thereof.

Example 2 Production of Chain-shaped Permalloy Powder

[0247] A nickel chloride hyxahydrate and ferric chloride were added topure water, to prepare a solution in which the concentrations of boththe components take values shown in the following Table 2: TABLE 3Concentration Component (mol/L) Nickel chloride 0.008 Ferric chloride0.032

[0248] After 100 ml of the solution was then added to 100 ml of the samereducing agent solution as that used in the example 1, followed byagitation at a temperature of 35° C. for one hour, a solid contentdeposited in the solution was filtered, rinsed, and then dried, toproduce a Permalloy [Ni (20%)—Fe alloy] powder.

[0249] When the shape of the obtained Permalloy powder was observedusing a scanning-type electron microphotograph, it was confirmed thatthe Permalloy powder had the form of fine metal particles being linkedin a chain shape, as shown in FIG. 9.

[0250] When the particle diameter of each of the metal particles and thediameter of the chain of the Permalloy powder were measured from theelectron microphotograph, the particle diameter of each of the metalparticles was approximately 50 nm, and the diameter of the chain wasapproximately 100 nm.

Preparation of Conductive Paste

[0251] 90 parts by weight of the chain-shaped Permalloy powder producedin the foregoing and 10 parts by weight of poly (vinylidene fluoride)serving as a binding agent, together with N-methyl-2-pyrrolidone servingas a solvent, were mixed, to prepare a conductive paste.

Formation of Conductive Film

[0252] A conductive film was formed on one surface of a polyimide filmserving as a base in the same manner as that in the example 1 exceptthat the above-mentioned conductive paste was used.

[0253] When the surface of the conductive film was observed by a metalmicroscope, it was confirmed that there were no irregularities on thesurface so that the surface was flat. The state of the surface wasestimated to be good. When the volume resistivity of the conductive filmwas measured, it was 2×10⁻⁴ Ω·cm.

Formation of Plated Coating

[0254] When Ni was then electroplated in the same manner as that in theexample 1 except that the conductive film was used, and the crosssection of a plated coating formed on the conductive film was thenobserved by the metal microscope, to find the ratio R_(ø) of the sizesof grains, it was 0.9 by the foregoing equation (1). Accordingly, thesizes of the grains hardly varied. It was confirmed that the platedcoating had a uniform crystal structure throughout the thicknessthereof.

Example 3 Formation of Conductive Film

[0255] The same conductive paste as that prepared in the example 1 wasapplied to one surface of a polyimide film serving as a base such thatthe amount of adhesion of a solid content would be 20 mg/cm², was thendried at 100° C. for four hours to remove a solvent while applying to acoating film a magnetic field having a strength of 79 A/m along itsplane, thereby forming a conductive film.

[0256] In the conductive film, a chain-shaped Ni powder was oriented inthe direction of the above-mentioned magnetic field, and was high in theconductivity in only the direction of the orientation in its plain. Thatis, the volume resistivity in the direction in which the chain-shaped Nipowder was oriented in the plane of the conductive film presented a lowvalue of 5×10⁻⁵ Ω·cm, while the volume resistivity in a directionperpendicular to the direction of the orientation in the same plane was3×10⁻³Ω·cm, and the volume resistivity in the direction of the thicknessof the conductive film was 2.5×10⁻³ Ω·cm.

[0257] When the surface of the conductive film was observed by a metalmicroscope, it was confirmed that there were no irregularities on thesurface so that the surface was flat. The state of the surface wasestimated to be good.

Formation of Plated Coating

[0258] After Ni was then electroplated in the same manner as that in theexample 1 except that a conductive terminal was attached to a portion atan end in the direction of the orientation of the conductive film toserve as a power feeding portion, the cross section of a plated coatingformed on the conductive film was observed by the metal microscope, tofind the ratio R_(ø) of the sizes of grains, it was 1.1 by the foregoingequation (1). Accordingly, the sizes of the grains hardly varied. It wasconfirmed that the plated coating had a uniform crystal structurethroughout the thickness thereof.

Comparative Example 1 Preparation of Conductive Paste

[0259] 90 parts by weight of a spherical Ni powder having an averageparticle diameter of 1.2 μm and 10 parts by weight of poly (vinylidenefluoride) serving as a binding agent, together withN-methyl-2-pyrrolidone serving as a solvent, were mixed, to prepare aconductive paste.

Formation of Conductive Film

[0260] A conductive film was formed on one surface of a polyimide filmserving as a base in the same manner as that in the example 1 exceptthat the above-mentioned conductive paste was used.

[0261] When the surface of the conductive film was observed by a metalmicroscope, it was confirmed that there were non-uniform irregularitiescorresponding to the size of the Ni powder on the surface so that thesurface was not flat. The state of the surface was estimated to be bad.When the volume resistivity of the conductive film was measured, it was8×10⁻⁴ Ω·cm.

Formation of Plated Coating

[0262] When Ni was then electroplated in the same manner as that in theexample 1 except that the conductive film was used, and the crosssection of a plated coating formed on the conductive film was thenobserved by the metal microscope, to find the ratio R_(ø) of the sizesof grains, it was 3.0 by the foregoing equation (1). Accordingly, thesizes of the grains widely varied. It was confirmed that the platedcoating had a two-layered structure comprising an area where the metalgrains were large and an area where they were small.

Comparative Example 2 Preparation of Conductive Paste

[0263] 90 parts by weight of a spherical Ag powder having an averageparticle diameter of 1.2 μm and 10 parts by weight of poly (vinylidenefluoride) resin serving as a binding agent, together withN-methyl-2-pyrrolidone serving as a solvent, were mixed, to prepare aconductive paste.

Formation of Conductive Film

[0264] A conductive film was formed on one surface of a polyimide filmserving as a base in the same manner as that in the example except thatthe above-mentioned conductive paste was used.

[0265] When the surface of the conductive film was observed by the metalmicroscope, it was confirmed that there were non-uniform irregularitiescorresponding to the size of an Ag powder on the surface so that thesurface was not flat. The state of the surface was estimated to be bad.When the volume resistivity of the conductive film was measured, it was1×10⁻⁵ Ω·cm.

Formation of Plated Coating

[0266] When Ni was then electroplated in the same manner as that in theexample 1 except that the conductive film was used, and the crosssection of a plated coating formed on the conductive film was thenobserved by the metal microscope, to find the ratio R_(ø) of the sizesof grains, it was 2.0 by the foregoing equation (1). Accordingly, thesizes of the grains widely varied. It was confirmed that the platedcoating had a two-layered structure comprising an area where the metalgrains were large and an area where they were small.

[0267] The foregoing results are summarized in Table 4: TABLE 4 SurfaceVolume conditions of resistivity of conductive film conductive filmR_(Ø) Example 1 Good 1 × 10⁻⁴ 1.1 Example 2 Very good 2 × 10⁻⁴ 0.9Example 3 Very good 5 × 10⁻⁵ 1.1 Comparative Bad 8 × 10⁻⁴ 3.0 Example 1Comparative Bad 1 × 10⁻⁵ 2.0 Example 2

Example 4 Preparation of Conductive Paste

[0268] 20 parts by weight of a chain-shaped Ni powder produced in theexample 1 and 80 parts by weight of thermosetting acrylic syrup which isliquid curable resin were mixed, to prepare a conductive paste. Theratio of the chain-shaped Ni powder to the total amount of both thecomponents was 2.5% by volume.

Preparation of Mold for Electroforming

[0269] A mother die IM1 which is the original form of a fine metalcomponent was formed on a conductive substrate IM2, as shown in FIG. 2A,utilizing X-ray lithography and electroplating.

[0270] Light curable resin [trade name XNR5507 manufactured byNAGASE&CO., LTD.] was then photo-cured after formation by reactiveinjection molding using the mother die IM1, to obtain a precursor 3′ ofa mold 3 having a fine recess 3 b which was the original form of athrough-hole pattern 3 a corresponding to the shape of the mother dieIM1 [FIGS. 2B and 2C]. The conditions of photo-curing were an exposuredose of 3 J/cm² and a pressure of 0.1 MPa.

[0271] After a conductive paste 1′ previously prepared was then appliedover a Cu substrate serving as a conductive substrate 2 such that thethickness thereof would be 5 μm using a blade coater, as shown in FIG.4A, the precursor 3′ was superimposed thereon with the recess 3 bpositioned on the lower side, and was then heated at 80° C. for twohours while being pressed at a pressure of 0.1 MPa, to cure thethermosetting acrylic syrup in the conductive paste 1′, thereby forminga conductive film 1 as well as fixing the precursor 3′ on the conductivesubstrate 2 (FIG. 4B).

[0272] The fixed precursor 3′ was polished until the thickness thereofreached 150 μm to penetrate through the recess 3 b, therebymanufacturing a mold for electroforming EM shown in FIG. 4C comprisingthe mold 3 having the through-hole pattern 3 a corresponding to theshape of the mother die IM1.

[0273] The fixing with the conductive paste was strong, so that theconductive substrate 2 and the mold 3 were neither shifted nor peeledoff, for example, even when the precursor 3′ was polished, as describedabove.

Production of Fine Metal Component

[0274] A conductive terminal was attached to the conductive substrate 2in the above-mentioned mold for electroforming EM, to serve as a powerfeeding portion, and the mold for electroforming EM was dipped in a Niplating bath prescribed as described below, to perform electroplatingunder conditions of a current density of 10 to 150 mA/cm² and a liquidtemperature of 40 to 60° C. TABLE 5 Ni plating bath (pH3.5˜4.5)Component Concentration Nickel sulfamate 450 g/L Boric acid  30 g/L

[0275] When the above-mentioned electroplating was performed for twohours, the through-hole pattern 3 a in the mold for electroforming EMwas filled with a plated coating 4′, as shown in FIG. 5B. After the moldfor electroforming EM was taken out of the plating bath, and wassufficiently rinsed, therefore, the plated coating 4′, together with themold 3, was polished, to line up the plated coating 4′ and the mold 3with each other to a thickness of 60 μm.

[0276] After the mold 3 was decomposed and removed by ashing using anoxygen plasma, the conductive film 1 was dissolved and removed by wetetching to remove the conductive substrate 2, thereby producing a finemetal component 4 corresponding to the shape of the above-mentionedmother die IM1.

[0277] When the surface roughness of the surface on the side of theconductive film 1 of the produced fine metal component 4 was measuredusing a 3D Surface Profiler [NewView5010™ manufactured by ZYGOCorporation], the center line average surface roughness Ra was less than0.5 μm.

[0278] When the tensile strength of the produced fine metal component 4was measured, to find the percentage of its measured value to thetensile strength of a fine metal component of the same size directlyformed by electroplating under the same conditions on the flat Cusubstrate as a strength ratio, it was 90%.

[0279] From the foregoing, it was confirmed that the fine metalcomponent 4 produced in the example 4 had good properties comprising asingle layered structure capable of exhibiting desired physical,mechanical, and electrical properties because grains of the originalparticle sizes which were identical to those in a case where it was madeto grow on a flat metal surface are produced from the early stages offilm formation, and had a uniform crystal structure throughout.

Example 5 Preparation of Conductive Paste

[0280] 20 parts by weight of a chain-shaped Ni powder produced in theexample 1, 20 parts by weight of a spherical Ag powder having an averageparticle diameter of 50 nm, and 60 parts by weight of thermosettingacrylic syrup which is liquid curable resin were mixed, to prepare aconductive paste. The ratio of the chain-shaped Ni powder to the totalamount of the three components was 2.5% by volume, and the ratio of thespherical Ag powder thereto was 2% by volume.

Preparation of Mold for Electroforming

[0281] After a conductive paste 1′ prepared as described above was thenapplied over a Cu substrate serving as a conductive substrate 2, asshown in FIG. 4A, a precursor 3′ which was the same as that formed inthe example 4 was superimposed thereon with a recess 3 b positioned onthe lower side, and was heated at 80° C. for two hours while beingpressed at a pressure of 0.1 MPa to cure thermosetting acrylic syrup inthe conductive paste, thereby forming a conductive film 1 as well asfixing the precursor 3′ on the conductive substrate 2 (FIG. 4B).

[0282] The fixed precursor 3′ was polished until the thickness thereofreached 150 μm to penetrate through the recess 3 b, therebymanufacturing a mold for electroforming EM shown in FIG. 4C comprising amold 3 having a through-hole pattern 3 a corresponding to the shape of amother die IM1.

[0283] The fixing with the conductive paste was strong, so that theconductive substrate 2 and the mold 3 were neither shifted nor peeledoff, for example, even when the precursor 3′ was polished, as describedabove.

[0284] Thereafter, a fine metal component 4 in the same shape and of thesame size was produced in the same manner as that in the example 4 usingthe mold for electroforming EM.

[0285] When the surface roughness of the surface on the side of theconductive film 1 of the produced fine metal component 4 was measured inthe same manner as described above, the center line average surfaceroughness Ra was less than 0.2 μm.

[0286] The tensile strength of the produced fine metal component 4 wasmeasured, to find a strength ratio, as in the foregoing, it was 95%.

[0287] From the foregoing, it was confirmed that the fine metalcomponent 4 produced in the example 5 had better properties than thosein the example 4 comprising a single layered structure capable ofexhibiting desired physical, mechanical, and electrical propertiesbecause grains of the original particle sizes which were identical tothose in a case where it was made to grow on a flat metal surface wereproduced from the early stages of film formation, and had a uniformcrystal structure throughout.

Example 6 Preparation of Conductive Paste

[0288] 75 parts by weight of a spherical Ag powder having an averageparticle diameter of 50 nm and 25 parts by weight of thermosettingacrylic syrup which is liquid curable resin were mixed, to prepare aconductive paste which is the original form of a second conductive film.The ratio of the spherical Ag powder to the total amount of both thecomponents was 20% by volume.

Preparation of Mold for Electroforming

[0289] A conductive paste containing a chain-shaped Ni powder which wasthe same as that prepared in the example 4 was applied over a Cusubstrate serving as a conductive substrate 2 such that the thicknessthereof would be 5 μm using a blade coater, as shown in FIG. 7A, and wasthen heated at 80° C. for two hours to cure thermosetting acrylic syrupin the conductive paste, thereby forming a first conductive film 1.

[0290] After a conductive paste 5′ containing a spherical Ag powderprepared as described above was then applied over the first conductivefilm 1, a precursor 3′ which was the same as that formed in the example4 was superimposed thereon with a recess 3 b positioned on the lowerside, and was heated at 80° C. for two hours while being pressed at apressure of 0.1 MPa to cure the thermosetting acrylic syrup in theconductive paste, thereby forming a second conductive film 5 as well asfixing the precursor 3′ on the conductive substrate 2 (FIG. 7B).

[0291] The fixed precursor 3′ was polished until the thickness thereofreached 150 μm to penetrate through the recess 3 b, therebymanufacturing a mold for electroforming EM shown in FIG. 7C comprising amold 3 having a through-hole pattern 3 a corresponding to the shape of amother die IM1.

[0292] The fixing with the conductive paste was strong, so that theconductive substrate 2 and the mold 3 were also neither shifted norpeeled off, for example, even when the precursor 3′ was polished, asdescribed above.

[0293] Thereafter, the fine metal component 4 in the same shape and ofthe same size was produced in the same manner as that in the example 4using the mold for electroforming EM.

[0294] When the surface roughness of the surface on the side of theconductive film 1 of the produced fine metal component 4 was measured inthe same manner as described above, the center line average surfaceroughness Ra was less than 0.2 μm.

[0295] The tensile strength of the produced fine metal component 4 wasmeasured, to find a strength ratio in the same manner as describedabove, it was 95%.

[0296] From the foregoing, it was confirmed that the fine metalcomponent 4 produced in the example 6 had better properties than thosein the example 4 comprising a single layered structure capable ofexhibiting desired physical, mechanical, and electrical propertiesbecause grains of the original particle sizes which were identical tothose in a case where it was made to grow on a flat metal surface wereproduced from the early stages of film formation, and had a uniformcrystal structure throughout.

Comparative Example 3 Preparation of Conductive Paste

[0297] 20 parts by weight of a spherical Ni powder having an averageparticle diameter of 1.2 μm and 80 parts by weight of thermosettingacrylic syrup which is liquid curable resin were mixed, to prepare aconductive paste. The ratio of the spherical Ni powder to the totalamount of both the components was 25% by volume.

Preparation of Mold for Electroforming

[0298] After a conductive paste 1′ prepared in the foregoing was appliedover a Cu substrate serving as a conductive substrate 2, as shown inFIG. 4A, a precursor 3′ which was the same as that formed in the example4 was superimposed thereon with a recess 3 b positioned on the lowerside, and was heated at 80° C. for two hours while being pressed at apressure of 0.1 MPa, to cure thermosetting acrylic syrup in theconductive paste, thereby forming a conductive film 1 as well as fixingthe precursor 3′ on the conductive substrate 2 (FIG. 4B).

[0299] The fixed precursor 3′ was polished until the thickness thereofreached 150 μm to penetrate through the recess 3 b, therebymanufacturing a mold for electroforming EM shown in FIG. 4C comprising amold 3 having a through-hole pattern 3 a corresponding to the shape of amother die IM1.

[0300] The fixing with the conductive paste was strong, so that theconductive substrate 2 and the mold 3 were also neither shifted norpeeled off, for example, even when the precursor 3′ was polished, asdescribed above.

[0301] Thereafter, an attempt to produce a fine metal component 4 in thesame shape and of the same size was made in the same manner as that inthe example 4 using the mold for electroforming EM. However, acontinuous plated coating which can function as the fine metal component4 was not formed until the thickness thereof reached the thickness ofthe mold 3 (150 μm).

Comparative Example 4 Preparation of Conductive Paste

[0302] 75 parts by weight of a spherical Ni powder having an averageparticle diameter of 1.2 μm and 25 parts by weight of thermosettingacrylic syrup which is liquid curable resin were mixed, to prepare aconductive paste. The ratio of the spherical Ni powder to the totalamount of both the components was 25% by volume.

Preparation of Mold for Electroforming

[0303] After a conductive paste prepared in the foregoing was appliedover a Cu substrate serving as a conductive substrate 2, a precursor 3′which was the same as that formed in the example 4 was superimposedthereon with a recess 3 b positioned on the lower side, and was heatedat 80° C. for two hours while being pressed at a pressure of 0.1 MPa, tocure the thermosetting acrylic syrup in the conductive paste. However,it was impossible to fix the precursor 3′ on the conductive substrate 2.

[0304] The foregoing results were summarized in Table 6: TABLE 6 Fixingof Ra Strength precursor (μm) Ratio (%) Example 4 Good <0.5 90 Example 5Good <0.2 95 Example 6 Good <0.2 95 Comparative Good — — Example 3Comparative Bad — — Example 4

1. A conductive paste characterized in that a metal powder having theform of a lot of fine metal particles being linked in a chain shape iscontained as a conductive component.
 2. The conductive paste accordingto claim 1, characterized in that the chain-shaped metal powder or eachof the metal particles forming the metal powder is formed of a metalhaving paramagnetism, an alloy of two or more types of metals havingparamagnetism, an alloy of metal having paramagnetism and other metal,or a complex containing metal having paramagnetism.
 3. The conductivepaste according to claim 2, characterized in that the whole or a part ofthe chain-shaped metal powder or each of the metal particles is formedby being deposited in a solution containing one type or two or moretypes of metal ions including metal ions having paramagnetism byreducing the ions to a metal using a reducing agent in the solution. 4.The conductive paste according to claim 3, characterized in that thereducing agent is a trivalent titanium compound.
 5. The conductive pasteaccording to claim 1, characterized in that the particle diameter ofeach of the metal particles is not more than 400 nm.
 6. The conductivepaste according to claim 1, characterized in that the diameter of thechain of the metal powder is not more than 1 μm.
 7. The conductive pasteaccording to claim 1, characterized in that the chain-shaped metalpowder and a binding agent are respectively contained as solid contents,and the content of the chain-shaped metal powder in the total amount ofthe solid contents is 5 to 95% by weight.
 8. A conductive filmcharacterized in that the conductive paste according to claim 2 isapplied over a base to form a coating film, a magnetic field is appliedto the coating film from a predetermined direction, to orient achain-shaped metal powder in the coating film in a predetermineddirection corresponding to said magnetic field, and the coating film issolidified to fix the orientation of the metal powder.
 9. A platingmethod characterized by comprising the steps of: applying the conductivepaste according to claim 1 over a base to form a conductive film; andmaking a plated coating grow on the conductive film by electroplatingusing the conductive film as an electrode.
 10. The plating methodaccording to claim 9, characterized in that the volume resistivity ofthe conductive film is not more than 1 Ω·cm.
 11. The plating methodaccording to claim 9, characterized in that the chain-shaped metalpowder in the conductive paste contains at least one type of metal whichis the same as that contained in the plated coating.
 12. A productionmethod for a fine metal component, characterized by comprising the stepsof: fixing a mold composed of an insulating material having a finethrough-hole pattern corresponding to the shape of a fine metalcomponent on a conductive substrate with a conductive film composed of aconductive paste intervened between the conductive substrate and themold according to claim 1, to form a mold for electroforming; and makinga plated coating selectively grow on a surface of the conductivesubstrate or the conductive film exposed at a portion of thethrough-hole pattern of the mold for electroforming by electroplatingusing the surface as an electrode, to form a fine metal productcorresponding to the shape of the through-hole pattern.
 13. Theproduction method for a fine metal component according to claim 12,characterized in that used as the conductive paste is one whichrespectively contains a chain-shaped metal powder and a binding agent assolid contents and in which the content of the chain-shaped metal powderin the total amount of the solid contents is 0.05 to 20% by volume. 14.The production method for a fine metal component according to claim 12,characterized in that used as the conductive paste is one containing thechain-shaped metal powder as well as a spherical metal powder having asmaller particle diameter than the chain-shaped metal powder.
 15. Theproduction method for a fine metal component according to claim 14,characterized in that used as the conductive paste is one whichrespectively contains the chain-shaped metal powder, a granular metalpowder, and a binding agent as solid contents and in which the contentof the chain-shaped metal powder in the total amount of the solidcontents is 0.05 to 20% by volume and the content of the granular metalpowder therein is 0.05 to 20% by volume.
 16. A production method for afine metal component, characterized by comprising the steps of: formingon a conductive substrate a first conductive film composed of theconductive paste according to claim 1 and a second conductive filmcomposed of a conductive paste containing a metal powder having asmaller particle diameter than a chain-shaped metal powder contained inthe first conductive film in this order, and fixing a mold composed ofan insulating material having a fine through-hole pattern correspondingto the shape of a fine metal component on a conductive substrate withboth the conductive films intervened between the conductive substrateand the mold, to form a mold for electroforming; and making a platedcoating selectively grow on a surface of the second conductive filmexposed at a portion of the through-hole pattern of the mold forelectroforming by electroplating using the surface as an electrode, toform a fine metal component corresponding to the shape of thethrough-hole pattern.
 17. The production method for a fine metalcomponent according to claim 16, characterized in that used as theconductive paste for forming the second conductive film is one whichrespectively contains a metal powder and a binding agent as solidcontents and in which the content of the metal powder in the totalamount of the solid contents is 0.05 to 70% by volume.